1) Field of the Invention
The present invention relates to a device for detecting a near end state of a roll of paper in the case of using paper drawn out from a rotatably held roll of paper, and more particularly relates to a detector which can be built into a printer, facsimile, or other recording apparatus which uses a roll of paper as a recording medium. Note that the term "near end state" means the state when there is only a small amount of the roll of paper remaining.
2) Description of the Related Art
For example, a printer mounted in a terminal of a POS (point of sale) system or register uses a roll of paper as a recording paper therefor. In this case, since the roll of paper is usually held in a location where it cannot be observed, the near end state of the roll of paper cannot be visually determined by the user. Accordingly, if the time for reloading a new roll of paper in the printer is missed, the data to be recorded is lost. To avoid this situation, a detector for detecting a near end state of a roll of paper is built into the printer, and is used to notify the user when the time has come to place a new roll of paper in the printer.
There have been two types of near end state detectors in the past; one is a type which detects the diameter of the roll of paper, while the other is a type which detects the weight of the roll of paper. The former type is used mainly when the roll of paper has a core, and indicates when the diameter has been reduced to a predetermined value due to the use of the paper from the roll. The latter type is mostly used when the roll of paper has no core, and indicates when the weight of the paper falls to a predetermined value due to the use of the paper from the roll.
In the above-mentioned printer, there is a problem in that the type of roll of paper which can be used is limited by the type of the near end detector built into the printer, even though any roll of paper, having a core or not, can be used for the recording. In particular, for example, when loading a coreless roll of paper in a printer having a built-in near end detector of the type which detects the diameter of the roll of paper, accurate detection of the near end state of the roll of paper is not possible and the time for loading the new roll of paper is missed. This is because when the remaining amount of a roll of paper without a core becomes small, the portion wound in a roll loosens and the diameter of the roll appears to increase, so it is not possible to accurately detect the diameter. On the other hand, even when loading a roll of paper with a core in a printer having a built-in near end detector of the type detecting the weight of the roll of paper, it is not possible to suitably detect the near end state of the roll of paper and therefore the time for loading a new roll of paper is missed. This is because it is not possible to accurately detect the weight of the roll of paper itself due to the weight of the core of the roll.